Current tires are being required to have higher performance, such as improved abrasion resistance in the tire tread portion and reduced rolling resistance (improved fuel economy).
With regard to reducing rolling resistance, a reduction in the amount of rubber leads to less energy loss, resulting in improved fuel economy. However, such a reduction in the amount of rubber causes a tread rubber to have a short distance between the groove bottom and the road-contact surface. This results in reduced abrasion resistance and therefore short tire life. Further, the tread groove bottom suffers a marked stress concentration, which easily results in cracking.
Meanwhile, in order to suppress cracking at the groove bottom, the amount of wax or antioxidant can be increased (Patent Literature 1). Unfortunately, however, this method allows the wax or antioxidant to precipitate on the tire surface during storage to cause discoloration into white or brown, spoiling the appearance of the tire.